Abstract

The optical path difference (OPD) of the supersonic mixing layer with convective Mach number 0.5 is measured using the nanoparticle-based planar laser scattering technique, and its short-exposure optical transfer function (OTF) is computed with the proper orthogonal decomposition (POD). The OPD is analyzed from the viewpoint of structure function, and remarkable power law behavior is found. The power exponent is computed and analyzed. Taking the advantage of POD in capturing the energy of a signal, we present a model for the temporal evolution of OPD, which combines the deterministic and random factors together. With this model, the short-exposure OTF of the mixing layer is computed and analyzed. The amplitude modulation is evident at low frequencies, and it is almost negligible at high frequencies. The imaginary part of OTF for the mixing layer with developed vortex structures is of considerable amplitude, and the phase modulation becomes important for image degradation. We compare this phenomenon with the early result in aero-optics and explain it with the non-Gaussian statistics of OPD.

© 2012 Optical Society of America

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